Lateral wells or drainholes are boreholes drilled out from a main well or borehole to improve communication with the formation. Conventional techniques for forming a lateral drainhole comprise the following multiple trips and steps:    Installation of Whipstock    Milling of casing window    Short-radius (a range between 6-18 m radius) drilling with a single or dual bent housing    Directional drilling    Deployment of a completion liner    Completion (more trips depending on drainhole conditions).
Multiple drainholes tied-in to a main cased or open well are expected to provide more effective oil recovery. However, a conventional drainhole construction in the manner described above requires costly and time-consuming operations, and it is also very difficult and complex in a thin hydrocarbon reservoir due to necessity of an entry curve from the main borehole to the lateral drainhole in the drilling trajectory. In unconsolidated formation, an entire length of the drainhole including both curved and straight portions may need to be cased and cemented with a completion liner to avoid collapse of the hole. This sort of completion requires multiple operations, sophisticated techniques and important costs according to nature of the drainhole. Various techniques have been proposed for systems and methods for forming drainholes or the like. These are discussed briefly below.
U.S. Pat. No. 6,167,968B1 and U.S. Pat. No. 5,392,858 disclose an apparatus for drilling holes in the steel casing of an oil or gas well, and drilling into the surrounding formations, including a number of components controlled by hydraulic fluid. This tool is available commercially under the trade name PeneDRILL by Penetrators Canada Inc. The tool is controlled and powered by fluid circulation from surface. It is capable to mill a 26 mm hole in the production casing and to drill a 17 mm hole in formation rock up to 2 meters in length. The tool contains two different drilling systems, one for metal casing and the other for formation rock. The tool is operable in the casing from 114 mm to 178 mm OD and is capable of four to eight tunnels per run.
The CHDT tool of Schlumberger comprises a downhole tool which uses a single drill bit and stem for casing milling and formation drilling. Further details are disclosed in U.S. Pat. No. 5,746,279, U.S. Pat. No. 5,692,565, U.S. Pat. No. 5,779,085 (and U.S. Pat. No. 5,195,588) and U.S. Pat. No. 5,687,806. The CHDT (Cased Hole Dynamics Tester) tool is a 108 mm diameter tool and is capable to drill a 7 mm diameter hole with 150 mm maximum penetration. The SCDT (Sidewall CoreDriller Tool), also of Schlumberger, is another similar tool with a 137 mm tool diameter. This tool cuts a cylindrical core with dimensions of 23 mm OD and 50 mm long from formation with up to 50 cores per trip. Neither the CHDT, SCDT or PeneDRILL tools are capable of installing liners or sealing them to casing in the main borehole.
U.S. Pat. No. 6,260,623 discloses an apparatus and a method for utilizing a flexible tubing string to form and isolate a lateral entrance opening to a lateral bore hole from a main borehole.
U.S. RE37,867E describes multiple operations and individual processes to complete a drainhole.
U.S. Pat. No. 5,074,366 describes a method and an apparatus for simultaneously drilling and casing a wellbore. The apparatus comprises an outer conduit string containing an inner drill string carrying a bit capable of drilling a wellbore with a greater diameter than the outer string. The drill string may be adapted to drill a nonlinear wellbore by offsetting the drill bit from the longitudinal axis of the outer string, and the drill bit is preferably retractable to permit withdrawal of the drill string after the wellbore completed, leaving the outer string of casing or liner in place.
U.S. Pat. No. 5,715,891 discloses a method for isolating each perforated or drainhole completion with the primary wellbore, for providing flow control means for each completion to permit selective testing simulation, production, or abandonment, and for facilitating selective re-entry into any cased drainhole for conducting additional drilling, completion, or remedial work.
U.S. Pat. No. 6,220,372 describes an apparatus for drilling lateral drainholes from a well casing with a flexible shaft having a bit at lower end to drill the drainholes in perpendicular to the main hole.
U.S. Pat. No. 6,263,984 describes a nozzle jet drill bits for drilling drainholes from a wellbore through a 114 mm or larger casing. U.S. Pat. No. 4,787,465 discloses a similar method and technique involving a hydraulic drilling apparatus and method suitable for use in a variety of applications including the drilling of deep holes for oil and gas wells and the drilling of vertical, horizontal or slanted holes, drilling through both consolidated and unconsolidated formations, and cutting and removing core samples.
U.S. Pat. No. 6,332,498 describes a completion method for drainholes. This invention includes a sleeve which can be positioned to give access to a window opening of the casing section in which the main casing is sealed from the liner section of a deviated wellbore to provide a hydraulic seal against passage of fluids from outside the casing of the wellbore into the main casing.
U.S. Pat. No. 6,648,068 describes a side tracking system including a window mill with a full-diameter cutting surface and a reduced diameter tapered cutting surface.
U.S. Pat. No. 6,662,876 describes an apparatus and a method for expanding tubulars in a wellbore.
U.S. Pat. No. 4,714,117 describes a method for completing a drainhole with casing, but without conventional cementing of the casing wherein in the drainhole portion of the wellbore a casing string composed of alternating casing subs and external casing packer subs is employed.
U.S. Pat. No. 4,402,551 describes a method and equipment to form horizontal cased and perforated drainholes for an underground, in-situ leach mining operation.
Lateral boreholes may need to be prevented from collapsing. Therefore, a completion liner has to be deployed and set. Slotted expandable liner (SEL) and solid expandable casing (SEC) are existing techniques for this function. SEL expansion is accomplished by opening up axial slots in the liner and by bending the steel (rather than deforming it). Unlike SEL, SEC expansion is achieved by yielding the pipe to a larger diameter, deforming it plastically. Similar to the slotted liner deployment, the solid expandable casing is typically expanded by moving an expansion mandrel through it. The expansion mandrel can either be mechanically pushed or pulled through the casing or hydraulically pumped. Both SEL and SEC are currently only available for boreholes of 114 mm diameter or above.
Most of the known systems are provided with electrical power via a wireline cable, for example the systems described in WO 2005/010318 and WO 2004/072437. However, this places a limitation on the power available for drilling and sealing. Also, most previous systems require the use of multiple tools for a complete drilling and completion operation.
This invention addresses these problems by using fluid flow as the power source and incorporating all functions in a single tool.